There are three different though related objectives of the proposed studies. First, we plan to investigate the binding characteristics of platelet-activating factor to both intact cells and membrane preparation, the role of the divalent cation, calcium, and the biochemical changes that are coupled to each receptor population. Second, we wish to elucidate the mechanism(s) by which phorbol 12-myristae 13-acetate inhibits the action of the platelet-activating factor and the role of protein kinase C in this inhibition. These include measuring the effects of the phorbol esters on: binding of platelet-activating factor, phosphoinositide hydrolysis, the dissociation of the G-protein, GTPase activities, and binding of nonhydrolysable GTP analogues. Third, we plan to characterize the effects of calcium channel blockers on binding of platelet-activating factor and the biochemical changes it produces.